1. Field of the Invention
The invention relates to a method and apparatus to allow irradiation of the eye for use in ophthalmology, refractive surgery and laser medicine.
2. Description of the Background Art
For our environment to be seen correctly, its optical image must be faultlessly projected onto the retina of the eye, and the individual surface curvatures and refractive index transitions of the eye must fit the spatial arrangement of receptors in the retina.
Where this faultless optical imaging is disrupted, existing visual deficiencies can be corrected traditionally with the help of glasses. A curved glass with specific refractive index, thickness and curvature relationships is then placed at a defined distance in front of the eye.
It is also known that relatively thin lenses, referred to as xe2x80x9ccontact lensesxe2x80x9d, can be put directly onto the eye""s cornea.
Apart from these corrections using auxiliary optical means, there is an option of obtaining changes to the eye itself by the use of surgery.
In cornea surgery, changes are made in cornea thickness by removal of tissue (ablation) or changes in its curvature by way of incision (keratotomy). Plastic cornea shaping represents another possible technique. It is accomplished by thermal interaction (thermokeratoplasty).
Because of its xe2x80x9cforemostxe2x80x9d position, the cornea is easily accessible for surgical treatment and for this reason appears to be researched intensively.
Laser cornea surgery is described in a multitude of documents, generally as laser ablation, mainly performed with excimer lasers, in other cases as thermal cornea shrinking, to induce a change in the curvature of the optical boundary surface.
An apparatus for ophthalmologic surgery is described in U.S. Pat. No. 4,718,418. It uses a scanned UV laser for controlled ablative photo decomposition of selected cornea areas. Irradiation density and exposure time are controlled in such a way that a desired ablation depth is obtained. Scan movements are appropriately coordinated to accomplish a desired change in surface shaping, which converts the cornea into a corrective lens.
The possibilities for eroding a surface with a laser apparatus, which contains means for selection and control of profile and dimensions of the area to be irradiated, with each laser energy pulse, leaving the beam""s energy density unvaried, but varying the dimensions of the exposed area between each two pulses, are described in U.S. Pat. No. 4,941,093.
In U.S. Pat. No. 5,334,190, methods and an apparatus for correction of optical vision defects are described. These use an infra-red radiation source and a focusing element to change the eye""s curvature by applying focused infra-red radiation to the collagenous cornea tissue in a controlled manner. This leads to heat-induced shrinking of the collagenous cornea tissue and, hence, to a change in cornea curvature.
U.S. Pat. No. 5,423,801 discusses a method and an arrangement containing a laser and a beam shaping mask to reshape the Bowman""s membrane without substantially penetrating into the eye""s stroma.
Various possibilities of varying the intensity of a cornea-eroding beam by means of erodable masks with pre-defined eroding resistance or graduated intensity filters, by means of selectively varying apertures or other mechanisms of selectively exposed areas are discussed in U.S. Pat. No. 5,505,723.
In U.S. Pat. No. 5,520,679, a refractive laser surgical method is described. It uses a compact low-priced laser system which integrates a computer-controlled scanner with a non-contact unit to perform both photo ablation and photo coagulation. The base system may incorporate flash lamps, diode-pumped solid state UV lasers (193-215 nm), compact excimer lasers (193 nm), free-running Er:Glass (1.54 microns), Ho:YAG (2.1 microns), q-switched Er:YAG (2.94 microns), multi-wave IR lasers (750-1100 nm) and (2.5-3.2 microns). In terms of the benefits of a non-contact scanning device, compactness, higher precision, reduced cost and greater flexibility are cited. Depending on the required beam overlap, ablation rate and coagulation pattern, the lasers are chosen to provide energies from 10 xcexcJ to 10 mJ with repetition rates between 1 and 10000, pulse lengths from 0.01 nanosecond to several hundred microseconds and spot sizes from 0.05 to 2 mm for use in refractive laser surgery.
Cornea reprofiling with a circular beam of ablative irradiation to correct refractive vision defects is shown in U.S. Pat. No. 5,613,965.
Methods for laser ablation and related devices are described in U.S. Pat. No. 5,624,436 and U.S. Pat. No. 5,637,109 and DE 19752949. They contain a laser beam required to work the object to a desired shape, an optical system to deliver the laser beam to the object to be treated, an aperture to vary the ablation area, a controller device for aperture motion, and a master controller to guide the controller device in shaping a curved surface with a required optical characteristic.
This allows the intensity profiles of excimer laser radiation to be improved for cornea ablation.
The possibility of modifying light beams or laser beams in their intensity distribution, in order to erode surfaces to pre-defined profiles using a rotating mask with one or more apertures, is shown in U.S. Pat. No. 5,651,784.
Devices and methods for laser surgery employing pulsed UV excimer lasers at 193 nm with energy densities above 20 mJ per cm2 and repeat rates as high as 25 pulses per second to direct their radiation through a mask onto the cornea tissue and initiate a process of ablative photo decomposition for the removal of tissue in a specified shape and to a specified depth are described in U.S. Pat. No. 5,711,762 and U.S. Pat. No. 5,735,843.
A possibility for combining competing spherical and cylindrical corrections on the cornea surface with the help of a variable iris aperture and a movable slit for reduction of myopia and astigmatism, is shown in U.S. Pat. No. 5,713,892.
To determine the center point location of the eye""s pupil after enlargement, a method and a device is given in U.S. Pat. No. 5,740,803.
Information on how to achieve exact control of the location, and determine the point of interaction of a surgical laser, and the controlling of the cornea profile during ophthalmologic surgery performed by means of an applanator, is contained in U.S. Pat. No. 5,549,632.
A favorably shaped beam profile, achieved with a specifically manufactured membrane which is opaque to laser radiation that has different thicknesses in different positions and is placed between the ablation laser and the cornea for surgical treatment, is represented in U.S. Pat. No. 5,807,379.
In WO 98/19741, a device and a method for thermal laser keratoplasty are outlined. They allow the areas of treatment on the cornea to be scanned to shapes such that regression is diminished. Desired changes in the cornea""s refractive power are created through locally selected, oblong, pointed photothermal shrinking patterns in the corneal collagen tissue as a result of laser scanning. The objective is to optimize the stress pattern in the cornea. To serve as surgical lasers, laser diodes featuring absorption lengths from 200 to 800 micrometers in the cornea tissue in a wavelength range of 1.3 to 3.3 micrometers are given as an example.
What all these methods have in common is that they influence the eye""s imaging performance by changing the curvature of optical boundary surfaces (cornea).
In DE 41 31 361 C2, an apparatus is described, which contains a UV radiation emitting excimer laser, a device to create a certain radiation pattern, imaging optics and a means for fixing the eye, with UV radiation selected in a wavelength range to be within the cornea""s absorption range and with an intensity that absorbed UV radiation can produce irreversible changes in the chemical structures in the cornea, thus allowing variation of the refractive index for visible radiation, but not allowing cornea tissue to be removed, and further that the device creating the radiation pattern accomplishes a position-dependent exposure of the cornea to UV radiation, which makes it possible to vary the refractive index depending on position. In addition, in DE 41 31 361 C2 it is reported that excimer lasers with their short wavelengths are able to break up chemical combinations.
High-energy ultra-violet radiation is known to imply a high mutagenic risk, particularly in the spectral range from 240 nm to 280 nm, which is due to resonant absorptions in RNA and DNA.
The task of the invention is to create a method and a device to allow vision defects to be corrected with simple means in a reproducible manner without involving any high-energy UV radiation with its inherent mutagenic risk.
A particular advantage of the invention is that it avoids mutagenic risks by exposing the eye lens to controlled therapeutic radiation in the long-wave UV-A range above cornea absorption and/or in the visible and/or the near infra-red wavelength range and/or the cornea in a defined way with treatment radiation above 1.3 micrometers, thus creating photo-induced local irreversible chemical changes in the eye lens""s substance and/or the cornea substance such that the refractive index and/or transmission properties of visible applied radiation is altered according to specified parameters, resulting in an essentially reduced vision defect level, where controlled therapeutic irradiation is accomplished through spatial structuring and modulation over time, as well as intensity control. The spatial structuring follows from spatial modulation and optical transformation.
Changes in the refractive index of the various eye lens regions are achieved efficiently and in a simple manner, using a device for irradiation of the eye, which consists of a radiation-emitting light source, means for radiation modulation over time, means for control of the radiation intensity, means for spatial modulation of radiation, optics to transform and shape the radiation as necessary for applying spatially modulated radiation to the eye, means for determining the orientation of the eye lens axis respectively the eye axis, and means for eye fixation and/or eye tracking, where the light source emits radiation that contains wavelengths for the treatment of the eye lens in the long-wave UV-A range above cornea absorption and/or in the visible and/or near infra-red spectral range and for the treatment of the cornea in the near infra-red spectral range above 1.3 micrometers, which are absorbed in the eye lens and/or the cornea to produce photo-induced chemical alterations in the eye lens""s substance and/or the cornea substance, which, if supported by adequate intensity control and radiation modulation over time, causes the eye lens and/or the cornea to change its refractive index for radiation, but causes no strong turbidity in the eye lens region and/or the cornea region due to pure amplitude portions, and further that the means for spatial modulation of radiation which is emitted by the light source are capable of impressing both a structured phase characteristic and a structured amplitude characteristic, further where the optics for transformation and shaping of radiation have at least one optical axis, and the radiation which is spatially modulated in terms of phase characteristic and amplitude characteristic is transformed into pre-defined segments of the eye lens and/or the cornea, which produces a desired equivalent variation in refractive index and/or transmission of the eye lens and/or of the cornea in terms of amount and spatial structuring.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.